Efficient allocation of network resources, such as available network bandwidth, has become critical as enterprises increase reliance on distributed computing environments and wide area computer networks. The widely-used TCP/IP protocol suite, which implements the world-wide data communications network environment called the Internet and is employed in many local area networks, intentionally omits any explicit supervisory function over the rate of data transport over the various devices that comprise the network. While there are certain perceived advantages, this characteristic has the consequence of juxtaposing very high-speed packets and very low-speed packets in potential conflict and produces certain inefficiencies. Certain loading conditions degrade performance of networked applications and can even cause instabilities which could lead to overloads that could stop data transfer temporarily.
In order to understand the context of certain embodiments of the invention, the following provides an explanation of certain technical aspects of a packet based telecommunications network environment. Internet/Intranet technology is based largely on the TCP/IP protocol suite, where IP (Internet Protocol) is the Open Systems Interconnection (OSI) model network layer protocol and TCP (Transmission Control Protocol) is the OSI transport layer protocol. At the network level, IP provides a “datagram” delivery service—that is, IP is a protocol allowing for delivery of a datagram or packet between two hosts. By contrast, TCP provides a transport level service on top of the datagram service allowing for guaranteed delivery of a byte stream between two IP hosts. In other words, TCP is responsible for ensuring at the transmitting host that message data is divided into packets to be sent, and for reassembling, at the receiving host, the packets back into the complete message.
TCP has “flow control” mechanisms operative at the end stations only to limit the rate at which a TCP endpoint will emit data, but it does not employ explicit data rate control. The basic flow control mechanism is a “sliding window”, a time slot within an allowable window which by its sliding operation essentially limits the amount of unacknowledged transmit data that a transmitter can emit. Another flow control mechanism is a congestion window, which is a refinement of the sliding window scheme involving a conservative expansion to make use of the full, allowable window. A component of this mechanism is sometimes referred to as “slow start.”
The sliding window flow control mechanism works in conjunction with the Retransmit Timeout Mechanism (RTO), which is a timeout to prompt a retransmission of unacknowledged data. The timeout length is based on a running average of the Round Trip Time (RTT) for acknowledgment receipt, i.e. if an acknowledgment is not received within (typically) the smoothed RTT+4*mean deviation, then packet loss is inferred and the data pending acknowledgment is re-transmitted. Data rate flow control mechanisms which are operative end-to-end without explicit data rate control draw a strong inference of congestion from packet loss (inferred, typically, by RTO). TCP end systems, for example, will “back-off,”—i.e., inhibit transmission in increasing multiples of the base RTT average as a reaction to consecutive packet loss.
A crude form of bandwidth management in TCP/IP networks (that is, policies operable to allocate available bandwidth from a single logical link to network flows) is accomplished by a combination of TCP end systems and routers which queue packets and discard packets when some congestion threshold is exceeded. The discarded and therefore unacknowledged packet serves as a feedback mechanism to the TCP transmitter. Routers support various queuing options to provide for some level of bandwidth management. These options generally provide a rough ability to partition and prioritize separate classes of traffic. However, configuring these queuing options with any precision or without side effects is in fact very difficult, and in some cases, not possible. Seemingly simple things, such as the length of the queue, have a profound effect on traffic characteristics. Discarding packets as a feedback mechanism to TCP end systems may cause large, uneven delays perceptible to interactive users. Moreover, routers can only control outbound traffic. A 5% load or less on outbound traffic can correspond to a 100% load on inbound traffic, due to the typical imbalance between an outbound stream of acknowledgments and an inbound stream of data.
In response, certain data flow rate control mechanisms have been developed to provide a means to control and optimize efficiency of data transfer as well as allocate available bandwidth among a variety of business functionality. For example, U.S. Pat. No. 6,038,216 discloses a method for explicit data rate control in a packet-based network environment without data rate supervision. Bandwidth management devices allow for explicit data rate control for flows associated with a particular traffic classification. In addition, certain bandwidth management devices allow network administrators to divide available bandwidth into partitions. These partitions ensure a minimum bandwidth and/or cap bandwidth as to a particular class of traffic. An administrator specifies a traffic class (such as FTP data, or data flows involving a specific user) and the size of the reserved virtual link—i.e., minimum guaranteed bandwidth and/or maximum bandwidth. Such partitions can be applied on a per-application basis (protecting and/or capping bandwidth for all traffic associated with an application) or a per-user basis (protecting and/or capping bandwidth for a particular).
While they operate effectively for their intended purposes, such static partitions, however, have certain limitations. When multiple users use a shared resource such as a cable modem connection or a single file server, TCP/IP does not ensure that an adequate share of the network resource is provided to each user. In order to provide a desired quality service to active users, a mechanism is necessary to make sure a single user does not dominate the shared resource. For example, the disparities in user access speeds among users of a network resource may result in a situation where users having high-speed access (e.g., DSL or cable modem access) “hog” available bandwidth associated with a network resource and, thus, crowd out users with low speed access (e.g., modem users). In addition, it may be desirable to limit the total number of active users that may access the shared resource at any point in time so that sufficient bandwidth exists to provide a satisfactory experience to each user.
Static partitions, discussed above, can be used to achieve these objectives. However, this mechanism requires an administrator to identify each potential user and configure a static partition for each. This mechanism becomes unwieldy, if not impossible to implement, given a large and/or unknown pool of potential users. For example, a network administrator would have to constantly update a static partition configuration as new users sign up for or drop a network resource. Moreover, each static partition requires memory space for the data structure that defines the partition and includes other required parameters, thus limiting the number of static partitions that can be created in any single bandwidth management device. In addition, while static partitions can limit the size of an allocation of the network resource to individual users, they do not limit the total number of users, which also affects response time or other quality of experience characteristics. Still further, static partitions are inefficient where the pool of potential users is generally much larger than the number of users actually using a network resource at a given time.
In light of the foregoing, a need exists in the art for a mechanism that recognizes new users and dynamically allocates to each user a partition controlling access to a network resource. In addition, a need in the art exists for a mechanism that allows for capping the number of concurrent users of a network resource. Embodiments of the present invention substantially fulfill these needs.